The present invention relates to thickened aqueous compositions containing an amphoteric surfactant, particularly to those compositions thickened with a synthetic, addition copolymer.
Cosmetic cleansers such as shampoos, soaps and the like consist of various ingredients including surfactants, preservatives and foam stabilizers, each of which performs a different specialized function, e.g., cleaning, foam boosting and the like. Often a harsh anionic or cationic surfactant, e.g., sodium lauryl sulfate or a quaternary fatty amine, is employed in such cleanser compositions to impart the required cleansing properties thereto.
Inasmuch as shampoo compositions containing such anionic or cationic surfactants are generally not sufficiently viscous for many applications, it has become a common practice to add a thickener thereto. Conventional thickeners employed heretofore include the cellulose ethers, e.g., methyl cellulose; certain synthetic addition copolymers such as polyvinyl acetate maleate or a copolymer of maleic anhydride, an alkyl vinyl ether and a hydrocarbon oxyalkylene vinyl ether; and combinations of a cellulose ether and a synthetic addition copolymer. See, for example, U.S. Pat. Nos. 2,645,615; 3,499,876 and 3,485,915. Alternatively, surfactant combinations such as the combination of sodium lauryl sulfate and a sulfonated amine, e.g., Sandopan TFL Conc. .RTM., are known to provide a thickened shampoo composition. See, for example, Journal of the American Oil Chemists' Society, Volume 49, June, 1972, Peter M. Hay, "Synergistic Interactions of Shampoo Ingredients", pages 343-345.
Unfortunately, to provide the desired cleansing properties, the shampoo often contains an amount of the cationic or anionic surfactant sufficient to render the shampoo composition relatively alkaline (e.g., pH of above about 9) or acidic (e.g., pH of below about 5) and to cause significant eye irritation. To alleviate the problems associated with the harsh cationic or anionic surfactant, amphoteric surfactants are employed in many shampoo formulations, particularly the so-called baby shampoos. The amphoteric surfactants have been found to provide suitable cleansing activity while greatly reducing eye irritation. Unfortunately, many of the conventional thickeners do not effectively thicken the shampoo compositions or other aqueous solutions containing amphoteric surfactants.
In view of the aforementioned deficiencies associated with thickening aqueous solutions of amphoteric surfactants, it remains highly desirable to furnish an aqueous composition of an amphoteric surfactant which is effectively thickened.